A linear motion guide used in a positioning section of, e.g., a machine tool, may include a component as shown in FIG. 16A and FIG. 16B, which is called linear rail guide (also called linear motion rolling bearing). The component is an assembly of a linear rail 30 and a sliding unit 31 which slides along the linear rail 30. The linear rail guide has a large variety in its size and shape, etc., and a wide range of the product is available from a number of manufacturers according to specific application requirements such as expected load, mounting attitude, etc.
Linear rail guides which are currently used widely can be divided into two types: One is called circulation type, in which rolling elements (not illustrated) such as balls and rollers in the linear rail guide circulate inside the sliding unit 31. The other type is called finite stroke type, in which rolling elements called cross roller guides stay captured by a retainer. For increased durability, both types make use of hardened steel such as a bearing steel for their linear rail 30 which provides a guide surface and for the rolling elements. As understood from the example in FIG. 16A, FIG. 16B, a ball screw mechanism and a linear rail guide are combined in parallel with each other, so that the ball screw mechanism will not come under a direct radial or moment load. This arrangement provides highly durable and accurate linear motion guides.
There are linear motion guides which do not make use of the linear guide rail: Patent Literatures 1 through 4 disclose techniques for implementing such linear motion guides by using vertical grooves and vertical guide surfaces formed on, e.g., an inner surface of a housing, etc., and a cam follower or other bearings which move along these vertical grooves and vertical guide surfaces. Also, Patent Literature 5 discloses a technique of implementing a linear motion guide by arranging a plurality of bearings in a circumferential direction of a housing, so that outer ring surfaces of these bearings make contact with a linear motion member disposed at a center.